Radak: All your counsel and witchcraft will not help you.

Malbim: For the present, there is no counsel to be saved.

Targum Yonasan: They are people who look at the Mazal in Shamayim. Rashi

Rashi: When the moon is Chadash (new), at the time of the Molad (when it is directly between the earth and sun).

Radak citing Ibn Ezra: They tell the future with their Chachmah. They do not look to see all that happens, only when the luminaries are joined ¹ . This is their expertise ² .

Rashi (from Sechel Tov Bereishis 37:36): They can see a little of what will come, but they do not know the full explanation. Therefore, it says "me'Asher" (part, and not Asher). Above (8:19) it says "ha'Metzaftzefim veha'Mahgim" - like birds that chirp, and they do not know about what. Radak - the verse teaches, the astrologers who predict future events - how did they not inform you of this evil that will come upon you, before it came, if they knew it?! Now, if they have a strategy to save you, let them save you!

Radak: Le'Chadashim refers to Alecha, and me'Asher Yavo'u refers back to v'Yoshi'uch.

Malbim: The astrologers cannot save you in the present, but at least let them save you from future evils!